Lightning arrester



1957- H. o. STOELTING LIGHTNING ARRESTEP.

2 Sheets-Sheet 1 Filed Sept. 50, 1953 FIG.I.

INVENTOR.

BY f d? 7 G W U W T S 0 N A M R E H A TTORNE Y Jan. 8, 1957.

H. O. STOELTING LIGHTNING ARRESTER 2 Sheets-Sheet 2 Filed Sept. 30, 1953FIG.2.

FIG.3.

FIG.4.

HERMAN O. STOELTING INVENTOR.

ATTORNEY United States Patent LIGHTNING ARRESTER Herman O. Stoelting,Milwaukee, Wis, assignor' to McGraw Electric Company, Milwaukee, Wis, acorporation of Delaware- Applicafion September 30, 1953, Serial No.383,311

Claims. (Cl. 31766) The present invention relates to excess-voltageprotective devices, and particularly, but not necessarily, to thosewhichare utilized for the protection of long transmission lines, or otherlines or apparatus which are subject to excess-voltage surges of longduration.

One commonly used form of excess-voltage protective devices has been thevalve-type lightning arrester, which is capable of passing heavydischarge-current when im pressed with voltages in excess of the ratedvoltage of theprotective device, and which is capable of substantiallyinterrupting said discharge upon the return of rated voltage-conditions.The valve-type element is normally positioned intermediate theline-to-ground terminals, and is normally out of circuit being separatedfrom the terminals by means of one or more sets of spark gaps. Thismaterial preferably comprises certain proportions of silicon carbide,sodium silicate and silicon dioxide.

On flow of surge current, due either to a lightning stroke or to aswitching disturbance, a conducting path is momentarily establishedthrough the arrester which, in the ideal'arrester, should be disruptedon termination of flow. of surge current. In this manner the arrestersimulates the action of a valve which is openedon occurrence of anabnormal voltage on the system to permit the flow ofsurge current toground, but which is automatically closed assoon as the excess voltageis dissipated.

It is the general practice to provide valve-type'lightning arrestersthat are hermetically sealed from the atmosphere. Ordinarily the valveelement does not generate appreciable amounts of gas, nor is there anydetectable chemical change in the valve element during the discharge ofthe surge current as long as the lightning arrester is ingood operatingcondition. However, when a lightning arresterfails, much of the: valvematerial is caused to fuse, and the material is formed into a conductingpathof comparatively low resistance to flow of power current. After theflow of surge current has ceased, the resistance of the failed arresteris not restored to it's normal or substantially infinite resistance toflow of current at power frequency, and a discharge or flow of. powercurrent takes place through it. The fusion of valvematerialparticlescauses a chemical change in the valve element with an accompanyingsudden release of copious amounts of gaseous products. Because of therigid seals on the arrester, the sudden rise of pressure may be highenough to cause the housing of the arrester to explode.

An explosion of a high voltage line-type arrester is generally much moresevere than the explosion of the smaller distribution-type arresters,since the housing and the seals of the line-type arresters are generallymuch stronger than the distribution-type arresters. Flying porcelainfrom the exploded arrester may endanger personnel and other nearbyequipment.

It is therefore an object of the present invention to provide a pressurerelief vent means for valve-type lightning arresters' that is arrangedto permit any gaseous ice 2, products from certain. chemical changesoccurring on failure of a lightning-arrester to be vented from thearrester to' prevent explosion from an accumulation of, the products.

It is another object of. the present invention to provide a pressurerelief vent means operatively associated with an electrical disconnectmeans for a valve-type-lightning arrester for relieving any pressurescreated on production ofgaseous products during chemical changesoccurring under a'failure of said lightning arrester.

It is, a further object of the present invention to provide apressurerelief vent means for a valve-type lightning arrester, which in itspreferred form is of an explosive cartridgertype circuit interruptingmeans that is in series gap relationship, with. the characteristic valvematerial of the arrester, and whichis. adapted to be exploded on heatingabove a predetermined temperature caused by excessive current.conditions due to failure of said valve material, and which will permitany gaseous products occurring on failure. to he released to atmosphere.

Foramore complete understanding of the nature and scope of the presentinvention reference may be had to the following detailed. description,taken in connection with the accompanying drawings, in which:

Fig. 1 is an elevational view, partly in section, of a valve-type.lightning arrester embodying the novel pres- SUIGJI'CllCf'. ventingmeans operating in conjunction with one terminal electrode of thearrester.

Fig. 2 is an enlarged fragmentary sectional view of the lower portion-ofthe valve-type arrester illustrated in Fig. 1.

Fig. 3 is a fragmentary sectional view of another embodiment of theventing'means.

Fig. 4:is' a fragmentary sectional view of a further embodiment of theventing means.

The lightning arrester, generally denoted by the reference. characterA,. is of the conventional valve type, and is preferably installed forthe protection of transmission and distribution equipment. Thevalve-type arrester comprises a tubularinsulating' housing 1 having aplurality of spaced skirts or petticoats 2 intermediate its ends. Thepetticoats' act as a means for extending the sparkover distance betweenterminals and provide a series of water sheds and dry areas in wetweather. 7 The insulating housing l" is preferably of porcelain coatedwith a uniform glaze, which facilitates self-cleaning when the arresteris exposed to dirtyatmospheres.

The bore of thetuhular housing is packed'with the conventionalcharacteristic valve element 3, which-may be provided under theteachings of the Stoelting Patent No. 2,305,577, issued December 15,1942. The valve-element generally comprises various proportions of amixture of silicon carbide, sodium silicate and silicon dioxide. Eachend of the valve element is preferably coatedwith a' metallic coating 4'to provide good electrical contact with the spark gap. The spark gapassembly is composed of a series of heavy, alloy disks 5 having high arcresistance. The disks are separated by ceramic spacers (not shown)preferably withsilvered faces, and are mounted on and held'i'n alignmentby a steatite rod 7; The spark gap assembly is preferably divided intotwo short sections, one of which is located at each end of the housing.This construction gives great mechanical strength and the ability towithstand the shocks of shipping and handling. It is to be noted thatlike reference characters have been used for like parts in this figureand also throughout the various other drawings.

The upper gap structure is held in position by constant pressure from acoil spring 8 between the gap assembly and the electrode sealing cap 9.Conducting, radially spaced straps 10- are provided to shunt the springand provide positive electrical contact between the sealing cap and thegap assembly.

An hermetic seal at each end of the arrester is preferably made bycompressing and retaining an insulating gasket between the sealing capand the flanged end portion of the housing 1. The upper end cap 16 ispreferably of cast malleable iron, and is cemented securely to thehousing to provide the means for mounting and making electricalconnections. Electrical connection is made at the terminal lugs 13 withconventional terminal clamps (not shown).

The lower end cap 20 is substantially identical to the opposite cap 16,but is provided with radially spaced vent openings 21, as shown in Figs.2, '3, and 4 for purposes hereinafter described. Terminal connections tothe lower cap 20 are made at the terminal lugs 22.

The preferred embodiment of the present invention will be described withparticular attention to Fig. 2, wherein the lower electrode sealing cap23 is provided with a centrally located support 24 having an opening 25arranged to freely and slidably receive a plug electrode 26 having aflanged portion 27 engaging a gasket member 28 interposed between theflange 27 and the support 24. The protruding end of the electrode 26preferably is threaded and engages the lower threaded end of a frangibletubular insulating member 29. The member 29 may be made of Bakelite orother insulating material adapted to rupture under certain pressureconditions exerted within its bore, as will be hereinafter described.The extremity of the electrode 26 is recessed and bored to provide ahollow portion 345 in which an explosive cap 31 is disposed. The upperportion of the frangible member 29 is threadingly engaged with aconducting electrode member 32 provided with a circumferential lipportion 33 surrounding, and spaced from, the portion of the electrode26. The upper portion of the electrode member 32 is provided with aperipheral flange 34 to receive the lower end of the coil spring 8.

A resistor 35 is provided to divert a few milliamperes of chargingcurrent which normally flows through the gaps of the high voltagearrester. The resistor is electrically connected to both the electrode32 and electrode sealing cap 23. Without this resistor the isolating gapwould be continually sparking-over and causing objectionable radiointerference. The resistance is maintained sufficiently high in orderthat in the event of an excess voltage surge a sparkover will occurbetween the lip 33 and the portion 30 of the electrode 26 to divert thesurge current from the resistor under normal action during anover-voltage condition.

Operation of the novel pressure is as follows:

If an excessively high current passes through the arrester valvematerial, it may cause a breakdown of this material and cause thegranular particles to fuse, and also bring about other collateralchemical changes. These chemical changes under the influence ofcontinuous current fiow provide reactions that often evolve copiousamounts of gaseous products that accumulate to create relatively highpressure conditions within the arrester housing. The products probablyinclude, in various amounts, water vapor, carbon dioxide and carbonmonoxide. These products are not dangerous in themselves, but do createforces within the hermetically sealed structure that will cause it toexplode and endanger personnel and nearby equipment. it has also beenfound that gaseous products are evolved when valve elements, such assilicon carbide, include other binders than sodium silicate. Theseproducts may be evolved at relatively high pressures during failure ofall types of valve arresters, including those using conventional ceramicbinders.

There is a definite time lag period during which the pressures are builtup, and if properly vented, this pressure may be discharged to theatmosphere before it may release venting means reach the danger point.In the past, there have been attempts to provide venting by means ofrupturable diaphragms and inherent weak structural sections in thehousing. However, it will be apparent that such devices only operateafter considerable time delay, and the pressures built up during thisdelay might be of suflicient force to cause damage on rupture of thediaphragms or the housing.

The main advantage of the present devices lies in the fact that therelief vent means is actuated by the excessive follow current whichflows through the arrester, and not by the pressures that might becreated. Thus, it is possible to vent the arrester before any of thehigh pressures are developed. That is, under normal operation, assumingthat a surge to which the arrester is subjected is not of such magnitudeas to destroy the valve characteristics of the valve element 3, then assoon as the line voltage returns to normal, the valve element willreduce the flow of current therethrough to a valve which will enable thegap to break the arc and thereby interrupt current flow through thearrester. However, occasionally surges occur on power lines which are ofsuch magnitude as to either destroy the arrester or change the valvecharacteristics of the material. When the coordinated characteristics ofthe gap assembly and the valve material have been altered by excessiveenergy discharges, the arrester may no longer be effective to interruptcurrent flow therethrough.

When the arrester is subjected to these damaging or destructive surgesor current flow, current passing between the electrode lip 33 and theconducting portion 30 of the electrode 26 will raise the temperature ofthe portion 30, and the heat thus generated will be conducted to theexplosive cap 31. Current flowing over a predetermined period of timewill cause the temperature of the cap 31 to be raised sufficiently toexplode the material in the cap and the expanding gases will drive thecap out of the portion 30 and rupture the frangible member 29. Uponrupture, the electrode plug 26 will be displaced to break the hermeticseal and provide a vent within the bore of the tubular housing 1 throughthe support 24 of the sealing cap 23. Thus, any gases created duringthis excessive current flow will be vented through the opening 25 of thecap 23 and out the vents 21 of the base portion 20, where they will bedischarged to the atmosphere.

Another embodiment of the present invention is disclosed in Fig. 3,wherein the novel pressure release venting means takes the form of acurrent responsive low melting alloy joint. In the embodiment of Fig. 3,the housing of one of the arresters is again hermetically sealed bymeans of the electrode sealing cap 23 and the gasket 15 mounted in alower end cap 20. The end cap 20 is again provided with radially spacedvent openings 21. This cap 23 is formed with an integral support 24having a centrally located opening 25.

The opening 25 is normally hermetically sealed by means of a resilientgasket member 40 interposed between the support 24 of the electrodesealing cap 23 and the headed portion 41 of the plug electrode 42 seatedin the opening. The plug electrode 42 has a portion extending within theopening and normally engaging an intermediate electrode 43. The plugelectrode 42 and the intermediate electrode 43 are joined by means of alow melting alloy joint 44, and are biased towards separation by meansof a coil spring 45. A tubular insulating housing 46, which may be ofBakelite, is positioned to rest on the support 24 of the cap 23 and isthreaded at its upper end to receive an upper electrode 47 makingcontact with the straps 10 and the spring 8. Vent ports 48 are providedin the wall of the housing 46.

It is again advisable to provide a resistor 49 between the electrodemembers 47 and 43 in order to dissipate the few milliamperes of currentwhich are normally discharging in the arrester, and would otherwiseinterfere with radio reception.

The embodiment of Fig. 3 operates in substantially the same manner asdescribed in connection with the embodiment of Figs. 1 and 2. That is,under normal operation, assuming that a surge to which the arrester issubjected, is not of such magnitude as to destroy the valvecharacteristics of the valve element, then as soon as the line voltagereturns to normal, the valve element will reduce, the flow of currenttherethrough to a value which will enable the gap to break the arc andthereby interrupt current flow through the arrester. However, on surgesthat might be of such magnitude, or of such current value, that wouldeither destroy the arrester or change the valve characteristics of thematerial, the arrester may no longer be efiective to interrupt currentflow therethrough.

The destructive current flow passing failed arrester to the upperelectrode 47, the resistor 49, the intermediate electrode 43; the alloyjoint 44 and to the plug electrode 42, will raise a temperature of thejoint 44 to cause it to melt. Inasmuch as the. plug electrode, 42 isbiased towards separation from the intermediate electrode 43 by the coilspring 45, the plug electrode 42 will be displaced from the positionshown in Fig. 3 to break the hermetic seal and expose the bore of thehousing 1 to the atmosphere through the opening 25 and the vent openings21. Any gases that might be created by chemical changes in the valveelement subsequent to excessive current flow, will be vented through theports 48 to be discharged to atmosphere.

Still another embodiment of the present invention will be described withparticular reference to Fig. 4, wherein a fragmentary sectional viewdiscloses the lower end portion of the arrester. The present embodimentutilizes a tempered glass which is critically responsive to heat, andwhich will shatter or disintegrate into many pieces losing itscompressive strength. More particularly, the plug electrode 59 isinserted in the opening 25 of the support 24 of the electrode sealingcap 23, and threadingly engages the lower portion of the insulatingglass member 51. The glass member rests on a resilient gasket 52, whichalso acts to provide a'hermetic seal for the interior of the housing 1-.An upper electrode member 53 threadingly engages the upper portion ofthe glass member 51 and makes electrical contact with the plug electrode56 through a resistor 54 interposed therebetween. A cushioning gasket 55is positioned between the upper elec trode 53 and the glass member 51. i

The operation of the embodiment of Fig. 4 is substantially identical tothe operation of the previously described embodiments. That is, on fiowof current in excess of predetermined value, the temperature of theelectrodes 50 and 53 will be caused to increase, and this continual risewill cause the high tempered glass to shatter. The lower plug electrode5t} will then be displaced to provide a vent through the opening 25 andthe electrode sealing cap 23. Thus, any gases created during flow ofthis excess current through the valve material, will be caused to bedischarged to atmosphere through the vent openings 21 in the end cap 20.

Highly tempered glasses of the nature described are well known in theglass industry, and can be tempered in such fashion as to shatter whenheated under certain conditions. The resistor 54 is again inserted todivert the few milliamperes of charging current normally flowing throughthe gap, and which might otherwise be the cause of objectionable radiointerference.

It is to be noted that although each embodiment of the novel pressurerelief vent means is disclosed as being associated with one particularsealing cap, it is within the scope of the present invention to providesuch means for either end of the arrester, or at both ends if preferred(not shown).

Although the pressure relief vent means has been described to operate incombination with valve-type arresters having spark gap assembliespreferably positioned at both ends of the-arrester, it will be apparentthat the device may be readily applied to arrester constructions wherethe gap assembly is located at a single end. The device is alsoapplicable to arresters having the gap elements disposed between axiallyspaced valve element portions (not shown). The arrester housing of suchstructures would naturally have to be vented to permit the gases toescape to atmosphere.

Arresters have been known to fail due to increased pressure interiorlyof the housing caused by the force of the are alone traveling in atightly constricted space, usually between the element and theinsulating housing. This pressure naturally needs to be vented for safeoperation of the arrester. The present pressure relief venting means, asdescribed, will permit an immediate release of such pressure responsiveto the excessive current flow substantially simultaneous with theStriking of the are.

It will be apparent that there has been provided by the presentinvention a novel pressure relief vent means in combination with aconventional valve type lightning arrester that will provide animmediate discharge of gases occurring with the housing of a failedlightning arrester simultaneously with the occurrence of that failure,in order to prevent an accumulation of gases that would otherwise causea damaging explosion with consequent destruction to personnel and nearbyequipment.

I claim:

1. In a lightning arrester comprising a tubular insulating housinghaving a bore, valve material contained within said bore and beingcapable of evolving gaseous products under pressure during predeterminedcurrent conditions, at least one set of gap electrodes, and a pair ofspaced-apart terminal caps, at least one of said caps defining anopening therein, the combination with an hermetic seal for said housingbore, a pressure relief vent means operatively associated with said oneof said terminal caps and comprising a plug-like member seated againstthe outside of said opening in sealing relation with said one cap, andhaving a portion extending inwardly through said opening, means withinsaid housing exerting tension on said inwardly extending portion tomaintain a sealing relation between said plug-like member and saidopening, a fast-acting thermal responsive actuator independent of saidreleasable electrode and instantly responsive to current due tosubnormal resistance of said valve material to suddenly release thetension on said inwardly extending portion to effect removal of saidplug-like member from its sealing engagement'with said one terminal,whereby said gaseous products may be discharged to the atmosphere.

2. In a lightning arrester comprising a tubular insulating housinghaving a bore, valve material contained within said bore and beingcapable of evolving gaseous products under pressure during predeterminedcurrent conditions, at least one set of gap electrodes, and a pair ofspaced apart terminal caps, at least one of said caps defining anopening therein, the combination with an hermetic seal for said housingbore, a pressure relief vent means operatively associated with said oneof said terminal caps and comprising a plug-like releasable electrodemember normally seated in said opening in releasable sealing engagementwith said one terminal cap to complete said hermetic seal and having aportion extending inwardly through said opening, means within saidhousing exerting tension on said inwardly extending portion to maintainthe sealing relation between said plug-like member and said opening, astationary electrode in electrical connection with said gap electrodes,said electrodes being in insulating relationship to provide a gap, aresistor in shunt relationship with said gap, and a thermal responsiveactuator independent of said releasable electrode and responsive tocurrent due to subnormal resistance of said valve material including anexplosive cap operatively associated with said last-men tioned electrodeto elfect release of the tension on said 7. inwardly extending memberresponsive to said predetermined current conditions, Whereby saidgaseous products may be discharged to atmosphere.

3. In a lighting arrester comprising a tubular insulating housing havinga bore, valve material contained Within said bore and being capable ofevolving gaseous products under pressure during predetermined currentconditions, at least one set of gap electrodes, and a pair of spacedapart terminal caps, at least one of said caps defining an openingtherein, the combination with an hermetic seal for said housing bore, apressure relief vent means operatively associated with said one of saidterminal caps and comprising a plug-like releasable electrode membernormally seated in said opening in releasable sealing engagement withsaid one terminal cap to complete said hermetic seal and having aportion extending inwardly through said opening, means Within saidhousing exerting tension on said inwardly extending portion to maintainthe sealing relation between said plug-like member and said opening, astationary electrode in electrical connection with said gap electrodes,said electrodes being in insulating relationship to provide a gap, aresistor in shunt relationship with said gap, and a thermal responsiveactuator independent of said releasable electrode and responsive tocurrent due to subnormal resistance of said valve material including afriable member operatively associated with said last-mentioned electrodeto efiect release of the tension on said inwardly extending memberresponsive to said current conditions, whereby said gaseous products maybe discharged to atmosphere.

4. in a lightning arrester comprising a tubular insulating housinghaving a bore, valve material contained within said bore and beingcapable of evolving gaseous products under pressure during predeterminedcurrent conditions, at least one set of gap electrodes, and a pair ofspaced apart terminal caps, at least one of said caps defining anopening therein, the combination with an hermetic seal for said housingbore, a pressure relief vent means operatively associated With said oneof said terminal caps and comprising a plug-like releasable electrodemember normally seated in said opening in releasable sealing engagementwith said one terminal cap to complete said hermetic seal and having aportion extending Q an inwardly through said opening, means within saidhousing exerting tension on said inwardly extending portion to maintainthe sealing relation between said plug-like member and said opening, astationary electrode in electrical connection With said gap electrodes,said electrodes being in insulating relationship to provide a gap, aresistor in shunt relationship with said gap, and a thermal responsiveactuator independent of said releasable electrode and responsive tocurrent due to subnormal resistance of said valve material including ahighly tempered friable glass member cperatively associated with saidlast-mentioned electrode to eiiect release of the tension on saidinwardly extending member responsive to said current conditions, wherebysaid gaseous products may be discharged to atmosphere.

5. in an excess-voltage protective device including an insulatinghousing, spaced apart electrodes, and valve material, the combinationwith an hermetic seal for said housing comprising a closure member insealing relationship With said housing and defining an opening therein,a releasable plug-like member normally seated in said opening in sealingrelationship with said closure member and outwardly movable towardsventing position, a thermal responsive actuator for said plug-likemember responsive to predetermined current conditions in said valvematerial and including a highly tempered friable glass member retainingsaid plug-like member in sealing relation, said glass member beingoperatively associated with said plug-like member to effect the removalof said pluglike member from the opening in said closure member therebyventing said hermetic seal on occurrence of said predetermined currentconditions causing at least a portion of said glass member todisintegrate.

References Cited in the file of this patent UNITED STATES PATENTS1,642,241 Golladay Sept. 13, 1927 2,276,054 Ludwig Mar. 10, 19422,315,320 Earle Mar. 30, 1943 2,551,858 Stoelting May 8, 1951 2,571,814Beck Oct. 16, 1951 2,586,285 Ackermann Feb. 19, 1952

